Journey's End

August 21, 2018

T102HAAS.303 Breaks Suspend

After upgrading my Asus Transformer Mini's BIOS to T102HAAS.303 suspend was completely broken. Closing the "lid" would cause some kind of suspend that cannot be disabled in software and from which Linux 4.15.0 cannot successfully resume from (actually it does resume but the display will stay blank).

This behaviour cannot be disabled in software by editing logind.conf or acpi-support or any of the solutions found on the web about disabling lid action. Messing about with acpi_osi didn't help either.

Downgrading from T102HAAS.303

If you are reading this after upgrading to T102HAAS.303 you probably want to downgrade. Unfortunately the firmware that ships with the computers, version 202, cannot be found on the Asus website. You can however find the 300 firmware if you click on "View all downloads" under the BIOS section. Download this file and put it on a FAT32 formatted USB drive then:

Reboot, hold then ESC to enter Setup

Find the Easy Update entry and press ENTER, starting the easy update program

Navigate to your USB drive, it will be FS0 or FS1

Locate the T102HAAS.303 file and press ENTER

When the dialogue complains that the build date is too old type the word risky on the keyboard

Select Yes on the dialogue that appears after

Wait for the computer to reboot

The key to this process is the word risky which is an undocumented feature that by-passes the build date check, allowing you to downgrade. You just type this in when the error dialogue appears, there will be no text box or anything.

Re-enabling Hibernation

Downgrading will re-enable Secure Boot, which disables hibernation on Linux. Just disable it and hibernation will work again.

August 06, 2018

Installation

Create a USB drive with a single FAT32 partition then extract the installation ISO into it using 7z:

7z x /path/to/ISO -o/path/to/usb

Note that there is no space between -o and the following path.

Plug in the USB drive then turn on the T102H while pressing the ESC key. This will allow you to enter the settings menu and allow you to boot from USB. Select installation and follow the instructions until asked to reboot.

Xorg Setup

An immediate problem is that the display is portrait by default. Additionally the modesetting driver is used which has worse performance than the intel driver. Fix both of these issue by placing the following file in /usr/share/X11/xorg.conf.d/99-transformer.conf:

i915

Backlight

Out of the box backlight doesn't work because of a module loading order issue [96571]. The easiest fix, found in the bug report thread, is to use dracut to remove the i915 module from initramfs so it loads after the PWM modules.

After rebooting /sys/class/backlight/intel_backlight/ should exist, indicating that backlight control is available.

Keyboard Backlight Control

Unfortunately while we can now control the backlight using programs like xbacklight, the screen brightness keys (fn+F5 and fn+F6) don't work. We can get around this by binding control-F5 and control-F6 to trigger xbacklight -dec 20 and xbacklight -inc 20 respectively to decrement/increment screen brightness by 20% per keyboard press.

Airplane Mode

Similar to the backlight control buttons the airplane mode button also doesn't work. The following script uses rfkill to toggle bluetooth and wifi on/off, effectively implementing airplane mode in software. I haven't found a way to disable bluetooth and wifi in hardware.

April 28, 2016

Carrier-phase detection is suppose to yield better timing information than tracking the pseudorandom code stream. The reason for this is supposedly that the higher frequency carrier allows for more accurate measurements of the mismatch between the generated pseduorandom code stream and the broadcasted one. This increase in accuracy comes from sharper peaks in the autocorrelation function.
Lets try this out:

It is clear that if you were trying to figure out the sample delay, you are much better off with the faster signal because the it is very obvious when you have the timing right. With the slower signal, you can be a little wrong and still get within a few pc of the correct correlation value.